rubber bellow/air spring crack/burse hole repair

If it were a patchable defect you'd need to apply the patch on the inside, but you can't.

What seems a likely cause of the crack/burst hole ?

chafing from rubbing against something close by?
Other mechanical damage?
Massive over pressurization ?
Old age rubber deterioration ?

My application only use the rubber with removable plates on both sides. So, I can access the inside.¡

R.Efendy

Check the condition of the rubber first.
If it is hard, brittle, or cracked then you need to replace the whole thing.
If it is a small hole less than a couple of mm and in a flat area, you might stand a chance.
But you need to know the cause before you even think about it.
Sounds like you have an external issue.

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P.E. Metallurgy, consulting work welcomed